319 research outputs found
4-tert-Butylpyridinium triiodide–4-tert-butylpyridine (1/1)
The title compound, C9H14N+·I3
−·C9H13N, consists of monoprotonated 4-tert-butylpyridinium cations and triiodide anions. The triiodide ion has near-symmetric linear geometry, with bond lengths of 2.9105 (4) Å (I—I) and a bond angle of 177.55 (3)° (I—I—I). For this room-temperature structure, the butyl group on the pyridine ring is disordered and has been treated as a rigid rotator, modeled in three separate positions with 1/3, 1/3, 1/3 occupancies. The cations assemble into dimeric forms by way of N—H⋯N hydrogen bonds
Anisotropic collisions of dipolar Bose-Einstein condensates in the universal regime
We report the measurement of collisions between two Bose-Einstein condensates
with strong dipolar interactions. The collision velocity is significantly
larger than the internal velocity distribution widths of the individual
condensates, and thus, with the condensates being sufficiently dilute, a halo
corresponding to the two-body differential scattering cross section is
observed. The results demonstrate a novel regime of quantum scattering,
relevant to dipolar interactions, in which a large number of angular momentum
states become coupled during the collision. We perform Monte-Carlo simulations
to provide a detailed comparison between theoretical two-body cross sections
and the experimental observations.Comment: 10 pages, 5 figure
Anisotropic expansion of a thermal dipolar Bose gas
We report on the anisotropic expansion of ultracold bosonic dysprosium gases
at temperatures above quantum degeneracy and develop a quantitative theory to
describe this behavior. The theory expresses the post-expansion aspect ratio in
terms of temperature and microscopic collisional properties by incorporating
Hartree-Fock mean-field interactions, hydrodynamic effects, and
Bose-enhancement factors. Our results extend the utility of expansion imaging
by providing accurate thermometry for dipolar thermal Bose gases, reducing
error in expansion thermometry from tens of percent to only a few percent.
Furthermore, we present a simple method to determine scattering lengths in
dipolar gases, including near a Feshbach resonance, through observation of
thermal gas expansion.Comment: main text and supplement, 11 pages total, 4 figure
Excitation spectrum of bosons in a finite one-dimensional circular waveguide via the Bethe ansatz
The exactly solvable Lieb-Liniger model of interacting bosons in
one-dimension has attracted renewed interest as current experiments with
ultra-cold atoms begin to probe this regime. Here we numerically solve the
equations arising from the Bethe ansatz solution for the exact many-body wave
function in a finite-size system of up to twenty particles for attractive
interactions. We discuss the novel features of the solutions, and how they
deviate from the well-known string solutions [H. B. Thacker, Rev. Mod. Phys.\
\textbf{53}, 253 (1981)] at finite densities. We present excited state string
solutions in the limit of strong interactions and discuss their physical
interpretation, as well as the characteristics of the quantum phase transition
that occurs as a function of interaction strength in the mean-field limit.
Finally we compare our results to those of exact diagonalization of the
many-body Hamiltonian in a truncated basis. We also present excited state
solutions and the excitation spectrum for the repulsive 1D Bose gas on a ring.Comment: 13 pages, 12 figure
Di-μ-pivalato-κ3 O,O′:O′;κ3 O:O,O′-bis[(methanol-κO)bis(2,2,6,6-tetramethylheptane-3,5-dionato)praseodymium(III)]
In the centrosymmetric dimeric title compound, [Pr2(C5H9O2)2(C11H19O2)4(CH3OH)2], the two praseodymium(III) atoms are eight-coordinate and are bridged by O atoms from the two pivalate anions. Each PrIII ion is further coordinated by two chelating 2,2,6,6-tetramethyl-3,5-heptanedionate (thd−) ligands and one methanol molecule. The distance between the two PrIII ions is 4.273 (5) Å. Intramolecular hydrogen bonds exists between the methanol hydroxy group on one PrIII atom and a chelating O atom of a thd− ligand coordinated to the symmetry-related PrIII atom
Drag force on an impurity below the superfluid critical velocity in a quasi-one-dimensional Bose-Einstein condensate
The existence of frictionless flow below a critical velocity for obstacles moving in a superfluid is well established in the context of the mean-field Gross-Pitaevskii theory. We calculate the next order correction due to quantum and thermal fluctuations and find a nonzero force acting on a delta-function impurity moving through a quasi-one-dimensional Bose-Einstein condensate at all subcritical velocities and at all temperatures. The force occurs due to an imbalance in the Doppler shifts of reflected quantum fluctuations from either side of the impurity. Our calculation is based on a consistent extension of Bogoliubov theory to second order in the interaction strength, and finds new analytical solutions to the Bogoliubov–de Gennes equations for a gray soliton. Our results raise questions regarding the quantum dynamics in the formation of persistent currents in superfluids
catena-Poly[1-butyl-3-methylimidazolium [[dichlorido(methanol-κO)(propan-2-ol-κO)lanthanate(III)]-di-μ-chlorido]]
The title compound, (C8H15N2)[LaCl4(CH3OH)(C3H7OH)], consists of one 1-butyl-3-methylimidazolium (BMI+) cation and one hexahedral tetrachlorido(methanol)(propan-2-ol)lanthanate anion. The LaIII ion is eight-coordinate, with the LaIII ion bridged by a pair of Cl atoms, so forming chains propagating along the a-axis direction. Each LaIII ion is further coordinated by two isolated Cl atoms, one methanol and one propan-2-ol molecule. The coordinated methanol and propan-2-ol molecules of the anion form O—H⋯Cl hydrogen bonds with the Cl atoms of inversion-related anions. The BMI+ cation froms C—H⋯Cl hydrogen bonds with the Cl atoms of the anion. The anions are located in the C faces of the triclinic unit cell, with an inversion center in the middle of the La2Cl2 ring of the polymeric chain
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